Injection-point flow control of undamaged polymer

ABSTRACT

A device that allows gradually regulation, i.e., non-destructively controlling the flow of injected polymer flooding enhanced oil recovery fluids at each point of injection, using: at least one conduit providing a variable length flow path combined with the centrifugal and other retarding or decelerative forces accessible to a formation engineer by configuring and otherwise arranging the spatial orientation and relative position of each section of such conduit, so as to achieve a never before attained degree of non-damaging flow control density within a compact space.

BACKGROUND

1. Field of the Invention

This application relates generally to controlling a flow of a polymer fluid injected for the purpose of enhancing oil recovery, and in particular to an apparatus and methods for doing so that delivers a sufficient quantity and quality of polymer fluid (including any gelled form thereof) without “shearing” or other degradation thereof.

2. Description of the Related Art

Traditional oil production methods result in only 20% to 30% of the original oil in place (OOIP) produced up the well hole. Polymer flooding, according to which a viscous body or “plug” of polymer sweeps oil through a formation in a desired direction, is one Enhanced Oil Recovery (“EOR”) technique allowing producers to recover an additional 15% to 20% of the OOIP. The conventional polymer flooding system consists of a source of polymer that is pumped under pressure to at least one injection well (or “point”) adjacent a production well toward which such plugs of flooding polymer form wave fronts that sweep oil through the formation. As explained in more detail below, the objective of sweeping oil toward a production well is complicated by the need to simultaneously control the velocity and volume of multiple wave fronts, flowing from different directions, and ostensibly through zones having different characteristics. Somewhat like an air traffic controller, with less detailed information, the formation engineer must apply best judgment respecting what is taking place sub-surface and coordinate the arrival of multiple polymer wave fronts on a common production point.

To further complicate matters, when EOR polymers are mixed, static shear mixers hydrate or activate the polymer. Once activated, the polymer fluid is pumped through a pipeline, typically to multiple injection points. To feed these injection points a supply “line” (typically a network of pipes) delivers the activated polymer to each well with a sufficiently elevated pressure to ensure the required flow to every point. The flow into each injection point is traditionally restricted in order to control the flow and deliver the correct volume flow into each well. A number of problems result if the composition and flow of the sweeping polymer is not carefully controlled, and each restriction risks damage to the already activated polymer due to abrupt changes in energy level during the transition from high to lower pressure. This is because a polymer is a large molecule formed by joining simple molecules known as monomers, and polymerization is the chemical reaction that joins monomers creating a polymer molecule. Effective liquid polymer activation depends on the application of high, but non-damaging, mixing energy to the neat, concentrated polymer. High mixing energy enhances the performance of emulsion polymer. However, re-exposing emulsion polymer to such high energy after the polymer is already fully hydrated or activated can damage the large molecules by “shearing” their attachment points that bond the water or carrier molecules. The flooding performance of a plug of polymer fluid depends on maintaining the bonds formed during activation, so the polymer's utility can be severely limited when overexposed to anything such as restrictions or impellers that can apply excessive mixing energy. Since the traditional flow controlling restriction is implemented using an orifice such as a choke, turbulence is introduced that causes shear and damages the polymer. Turbulence involves the collision of molecules such that bonding points are re-exposed and may be damaged. Consequently, traditional flow control devices such as chokes tend to breakdown the polymer fluid—reducing its viscosity below a useful level. The vast majority of prior art in the EOR polymer flooding industry has concentrated on teaching variations of flow control based on the orifice and similar restrictive devices.

In a given oilfield of injection wells, driving polymer towards a specified production well, the formation engineer needs to be able to apply the available polymer and injection resources in an efficient manner so as to optimize the sweeping effect and related production result within those limitations. Accordingly, it is also desirable to individually adjust the rate of flow of an undamaged polymer plug at each injection point, in order to accommodate the unique characteristics of the formation at each injection point. Whereas at a given injection point the resistance to flow may be very low and another point (within the same field) resistance very high, from a production perspective it would be ineffective to apply the same pressure of polymer fluid supply to both injection points because the fluid will follow the path of least resistance such that the low resistance injection point will consume the majority of the polymer resources leaving less to inject at the high resistance injection point. Accordingly, it is necessary to, in some manner, restrict the flow into the low resistance injection point while also maintaining a specified flow into the high resistance injection point, despite both being supplied from a common source of polymer and pressure. The traditional means of restricting flow to the low resistance injection point is to “choke” off the flow of polymer at the injection point, however that results in a sudden change that causes turbulence that is harmful to the polymer. It is therefore desirable to have means to individually control the rate of flow of the polymer fluid at each injection point, but without damaging the condition of that polymer.

One method for reducing shear degradation while maintaining pressure and flow control, is described in U.S. Pat. No. 4,204,574 respecting the insertion of shear degradable aqueous polymer solutions into a polymer thickened flood wherein a series of pumps are used in a multi-branch system. This method purports to address the problem of shear being induced by individual control over a common polymer source, but disadvantageously relies on a number of expensive hydraulic drivers and pumps to maintain the unique rate of injection required at injection point receiving fluid from a fluctuating common master branch.

More recently the internal “friction” (or adhesion to the inside) of pipes has been recognized as a prospective means of controlling flow. One example of such may be found at link: http://www.fabtechinc.net/rexasp.aspx. It is believed that the use of long lengths of small diameter hydraulic hose have also been applied to control polymer flow. These recent systems appear to rely on the long known but inadequately applied principle of drag induced by the relative motion of a viscose fluid inside a conduit. Disadvantageously, the linear array or cage of pipes comprising even this most relevant of the known prior attempts is bulky and inefficient making use of simple lengths of pipe threaded together, which are not suitable for sour water leak exposure applications. Within the large physical space required (resulting in a “low density” of flow control) to operate these rudimentary devices the amount of drag that may be induced using their linear form of flow controller is limited to that achieved by taking into account the Reynolds Number of the flow and the internal roughness of the selected pipe together with that resulting from mismatched fittings (both couplings and valves)—that collectively create the risk (above a characteristically relatively low flow rate) of the creation of polymer damaging turbulence such that the volume of flow through their conduit is limited, thereby in turn limiting the maximum flow to at least some of the injection points. All such restrictions of flow lead to a “weakest link” problem being imposed on the injection plan that the formation engineer would prefer to implement, such that the pace of combined sweep of the polymer wave fronts is also reduced thereby directly reducing the potential production rate of the entire injection site, because the available polymer and injection resources are applied in a less than optimal manner. Oilfield resources are expensive, such that it is desirable to identify every practical improvement to polymer injection flooding control equipment, which improvements would result in more oil being produced per unit time, in turn permitting those resources to be taken out of service or moved to a new location sooner. A more sophisticated and reliably predictable apparatus is desirable to give the EOR formation engineer the degree and flexibility of flow control required for optimal production.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention may, for example, include a device for non-destructively controlling the flow of polymer flooding EOR fluids at each point of injection at a well-site using a conduit providing a variable length flow path combined with the centrifugal and other retarding or decelerative forces accessible to a formation engineer by configuring and otherwise arranging the spatial orientation and relative position of each section of such conduit, so as to achieve a never before attained degree of non-damaging flow control density within a compact space.

Advantageously, such may provide for synchronized multi-point flow control over a polymer flood so as to coordinate multiple polymer wave fronts from different directions to arrive in a timely manner acting on a common production point, thereby implementing a site flooding plan in an efficient manner to make the optimal use of polymer possible. Further, such may allow use of a compact apparatus which employs tightly configured seamless conduit and smoothly joined elements that avoid inducing turbulence despite the continuous deceleration caused by passing the polymer fluid through coils of pipework densely assembled in close proximity and using carefully matched internally machined fittings wherever required.

According to one aspect, an apparatus may enable a formation engineer to relatively finely tune the flow of polymer fluid required to an injection point sweeping oil towards a defined production well, and then permit a relatively less experienced operator to implement a substantially optimal injection plan, based on installing and operating one such apparatus per injection point. Such may advantageously allow the formation engineer and operators of an injection well-site to refine and/or customize the flow pattern of the site so as to supply a sufficient volume of polymer fluid to each high resistance injection point while simultaneously limiting the volume of polymer flowing into each low resistance injection point, without introducing harmful turbulence at any injection point. When the polymer fluid is delivered to all injection points without degradation, the polymer fluid is better able to sweep oil through the reservoir. If appropriate volumes of polymer fluid synchronously travel through their respective flow controllers and then their respective portions of the formation so as to arrive at their designated locations in a timely manner. The combined sweeping effect of the compressive plugs of polymer fluid may move the oil through the reservoir toward a common production point in a more efficient (i.e., no fingering or breakthrough) fashion than otherwise possible. With the many factors that a formation engineer must accommodate and control in order to optimize production at each injection site, it may be advantageous to install the apparatus at each injection point to provide individually adjustable means for controlling flow without introducing turbulence. The apparatus may permit operators to control the volume of laminar flow of polymer fluid to a particular injection point by varying the effective length and spatial orientation of the drag inducing conduit through which the polymer fluid is required to pass for delivery to that injection point. Much like the “cars” on a roller coaster, the stream of activated polymer fluid moving inside a conduit is subjected not only to the frictional drag between the “wheels and tracks”, corresponding to the tendency for a viscous fluid to adhere to the inner walls of the conduit, but also to the decelerative forces that absorb energy from the stream of polymer fluid as the stream changes direction passing around each curve. Such may be particularly enhanced by use of a helical structure formed by the tubular coils. By this novel means of using the combination of friction and decelerating coils or other loops to restrict the flow of EOR flooding polymer fluid—excess energy is gradually dissipated to avoid turbulence such that the attachment points of the polymer molecules are not exposed to sudden change and thereby sheared. Advantageously, the low resistance injection points are supplied by longer and/or more frequent and tightly looped paths of fluid delivery conduit that delay the arrival of the required volume of polymer fluid into the formation so as to permit an operator to better coordinate delivery with slower moving polymer traveling through high resistance points.

Accordingly, there may be provided a compact device for reliably adjusting and controlling flow rate at the point of injection by allowing the operator to introduce or omit different series of coils of differing lengths simply by turning any one or all of the bypass valves in the fluid circuit. Not only does such an apparatus permit operators to accommodate the fluid flow factors of: viscosity, density, velocity, active conduit length, inner diameter of available conduit, internal roughness of conduit, transient changes in temperature, and the relative position of supply and discharge manifolds and lines, but it also takes into account and makes use of the centrifugal forces and other naturally decelerative effects of the combinations of possible spatial orientation that are available to the creative engineer within the efficiently limited volume of space. Thus the apparatus may accordingly be constructed, transported, and housed less expensively than otherwise possible.

In order to overcome the many efficiency disadvantages of the prior art it is necessary to expedite and coordinate delivery of polymer fluid to each injection point in sufficient quantity without shearing. According to at least one embodiment, there is provided a novel method for using conduit so that rather than restrict polymer flow instantaneously, the required pressure reduction is introduced without the attachment points of polymer molecules being exposed to sudden change and sheared. In at least one embodiment, an apparatus introduces resistance to flow thereby gradually reducing velocity (and thus the force of collisions at the molecular level) by adjusting the number of loops of pipe that increase back pressure (or drag) as the polymer flows through the loops. Several loops may be connected in series with bypass valves permitting each coil of tubing to be used alone. The back pressure of each loop or coil is caused primarily by the viscosity of the polymer fluid as the polymer fluid resists flow, since when fluid flows through a tube, the fluid typically flows fastest at the middle of the tubing and slowest at the outer edge where the fluid makes contact with the walls of the tubing. A boundary layer typically forms in the fluid proximate or at the wall of the tubing in which the flow may be negligible. Thus, the only movement of the fluid proximate the wall may be when molecules hop over each other. Faster flowing fluid towards the middle of the tubing next to slower moving fluid at the edge of the tubing may cause a rolling of the fluid molecules. The energy required to move the fluid as it changes direction (accelerating around each coil) also causes pressure loss as the fluid flows along the tubing. The losses resulting from each bundle of coil may be calculated and reliably predicted once all the variables influencing flow are defined. The configuration of a flow path defined by the apparatus may be either adjusted to accommodate local conditions, or a custom compact embodiment of the apparatus may be assembled to address the specific conditions present at a given well-site where a particular injection plan is to be implemented.

According to at least one aspect, there is further provided a method of manufacturing such an apparatus incorporating the use of joint-less welded tubes to prevent deadly leaks of sour water. The present method of manufacturing and the present apparatus may further include a heater that protects aqueous polymer against freezing, and a housing that facilitates leak detection and protection against mechanical damage during transportation and operation.

According to one aspect there is provided a flow control apparatus to control a flow of a stream of moving polymer fluid during injection to be used in a well to enhance the recovery of oil from a production well. The apparatus may be summarized as including: an inlet fluidly coupled to a source of polymer fluid under pressure to receive the polymer fluid; an outlet fluidly coupleable to an injection point; and at least one conduit that provides a selectively variable length flow path fluidly coupled between the inlet and the outlet, having internal friction creating drag between the conduit and moving polymer fluid, to controllably decelerate the rate of flow of the stream of polymer fluid. The apparatus optionally further includes at least one valve means fluidly coupled to the conduit, to control the (portion of the) length of the conduit through which the stream of moving polymer fluid pass before reaching the outlet. The conduit may include: a first tube fluidly coupled to the inlet and a second tube selectively fluidly coupleable between the first tube and the outlet. The conduit or apparatus may include at least one valve operable to selectively fluidly coupled the second tube into and out of the flow path through which the stream of polymer fluid passes between the inlet and outlet, thereby controlling the length of the fluid flow path defined by the conduit. The conduit or apparatus may include a bypass mechanism operable to divert the flow of the polymer fluid to the outlet. The first and second tubes may each optionally comprise a helical coil of round tubing or connected lengths of pipe, to enhance the deceleration of the polymer fluid within a more compact space. The helical coils or pipes may be concentrically arranged with respect to one another. The apparatus may optionally further include: a heater and a housing, for permitting aqueous streams of polymer fluid to be injected during cold weather.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings.

Various embodiments, in order to be easily understood and practiced, are set out in the following non-limiting examples shown in the accompanying drawings.

FIG. 1 is an end isometric view of a compact apparatus for controlling the flow of a stream of polymer (fluid or gel) comprising four coils of tubing that form a conduit providing a variable length flow path, according to one illustrated embodiment.

FIG. 2 is an end isometric view of the apparatus of FIG. 1, suitable for cold weather operation further comprising heating and an insulated housing, according to one illustrated embodiment.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known formulations, process steps, and structures associated with polymer flooding EOR have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments. It is to be understood that all joints, fittings, valves, tees and couplers employed are preferably of a similar internal diameter (ID) to the selected conduit for smooth transitions, or during fabrication one will radius the corners and internal diameter to match and avoid turbulence. Similarly, the conduit material may in theory be anything since internal diameter and roughness are variables taken into account in unit design calculations that make an operational custom built flow controller possible. It is a matter of determining how much energy must be extracted from the flow of polymer to achieve the required rate of injection at the injection well head. However, in practice it is the local regulations that may dictate the selection of materials, not the physics. The materials actually used in the field are determined by the composition of the substance flowing through them. For example, using sour water to hydrate the polymer makes stainless steels a good choice to meet environmental protection requirements. However, when the water polymer mix is non-toxic and non-polluting, then even if it leaked one could safely use a suitable form of plastic pipe as the drag inducing conduit.

Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, which is as “including, but not limited to.”

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Reference is to be had to FIGS. 1 and 2 in which identical reference numbers identify similar components.

As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. The headings and Abstract of the Disclosure provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

It is to be understood that in accordance with Newton's second Law, centrifugal force is an outward force associated with motion along a curved path, which incorporates rotation about some (possibly non-stationary) center. Centrifugal force is one of the so-called pseudo-forces (also known as inertial forces), so named because, unlike fundamental forces, they do not originate in interactions with other bodies situated in the environment of the element upon which they act. Instead, centrifugal force originates in the curved motion of the frame of reference within which observations are made. As it passes through the conduit(s), a plug of fluid flowing along the curved path of a helical coil of tube as the fluid's “rotating” frame of reference experiences various inertial forces. Consequently, according to the embodiments described herein which may be implemented using pipes as the conduit element, the rate of flow of polymer is affected by all of: the viscosity, density, and velocity of the polymer fluid; the implementation of a pipe layout that includes looping rises and/or falls; the location of supply and discharge containers relative to the pump position; the length, inner diameter, and internal roughness of each element of pipe deployed as the operational pipework; and any weather or location related changes in polymer fluid temperature that influence the viscosity and/or density of the polymer fluid at the location where the apparatus is operated. Fluids in motion are subjected to various resistances that are due to friction. Within the conduit's contemplated curved frame of reference, friction will occur between the fluid and the pipework, but friction also occurs within the fluid as sliding between adjacent layers of fluid takes place. The friction within a fluid is due to the viscosity of the fluid. When fluids have a high viscosity, the speed of flow tends to be low and resistance to flow becomes almost totally dependent on the viscosity of the fluid, which condition is known as ‘laminar flow’. These are all factors that the design and formation engineers takes into account to control flow.

It is further to be understood that polymer fluid head resistance may be calculated using the equation: h=f(L/d)×(v²/2 g) where: h=head loss (m); f=friction factor; L=length of pipe work (m); d=inner diameter of pipe work (m); v=velocity of polymer fluid (m/s); and g=acceleration due to gravity (m/s²).

Referring to FIG. 1 there is illustrated a flow control apparatus, denoted generally as 100, for use with a stream of polymer fluid moving in the laminar flow range up to 25 centipoise viscosity, and applied during injection to enhance the recovery of oil from a production well. According to at least one embodiment of the apparatus, a lower tube coil 110 of coiled tubing is fluidly coupled to a bank of upper tube coils 120, 130, 140 of tubing of varying lengths here connected in series. For example, in the embodiment illustrated the coils total 300 feet in length with tube coil 110 being 160 feet long, tube coil 120 being 80 feet long, tube coil 130 being 40 feet long, and tube coil 140 being 20 feet long. Lower tube coil 110 is coupled to said upper tube coils through header 150 that has any suitable inlet 160 and outlet 200. The tubing may be mounted on any suitable frame.

Header 150 receives a stream of polymer fluid (not shown) via inlet 160 and such flow through drag inducing apparatus 100 is initiated or terminated via any suitable isolation valve or valves (not shown) that permit said stream of polymer fluid to fluidly couple to an injection point (not shown) through outlet 200. It is to be understood that isolation valves may be, but are not necessarily, installed on the apparatus side of either or both of inlet 160 and outlet 200.

As a stream of polymer fluid flows through drag inducing apparatus 100, there are a plurality of bypass valves (here 210, 220, 230, and 240) that permit an operator to vary the length of the total conduit through which said stream of polymer fluid flows between inlet 160 and outlet 200.

According to one embodiment, as illustrated by apparatus 100, when bypass valve 210 is open, the stream of polymer fluid, taking the path of least resistance, flows through header 150 without entering lower tube coil 110. However, when bypass valve 210 is closed, said stream of polymer fluid is diverted at tee (T) coupling 215 through lower tube coil 110 and fluidly re-coupled to header 150 at tee (T) coupling 225 from where the polymer fluid may flow through apparatus 100 towards outlet 200. Similarly, bypass valve 220 when open permits the stream of polymer fluid to bypass tube coil 120. When bypass valve 220 is closed, the stream of polymer fluid is diverted through tube coil 120. Tube coil 120 may, for example, be approximately 80 feet long. Thus, if both bypass valves 210 and 220 are closed the stream of polymer fluid must flow through both tube coil 100 and tube coil 120. Such may, for example, cause the stream of polymer fluid to flow through 160 feet of tube coil 110 plus 80 feet of tube coil 120, which is a total of 240 feet of drag inducing coil. Such may gently slow the laminar flow of the stream of polymer fluid without inducing harmful turbulence. Similarly, bypass valves 230 and 240, when open, permit the polymer stream to bypass their respective tube coils 130 and 140. When closed, bypass valves 230 and 240 may be used by an operator to incrementally increase the drag inducing path length. For example, such may allow the operator to increase the flow path length by 40 feet and 20 feet, respectively, to further slow the flow of any stream of polymer fluid to the injection point to which apparatus 100 has been fluidly coupled. The amount of drag induced in the particular flow path is determined by many factors over which an operator has control.

It is contemplated that if an operator knows in sufficient detail the precise characteristics of the formation and the hydrocarbons at a given well-site, then a custom flow controller can be designed and assembled to optimally serve each particular well. Advantageously, the apparatus described herein permits an operator to incrementally adjust flow control to accommodate less than perfect information respecting well characteristics, as well as based on changes to injection point behavior over time and in different weather conditions. It is to be understood that the selection of each of: 1) a total of 300 feet in available coil length; 2) the particular lengths (i.e., 160, 80, 40, and 20 feet) of each coil; 3) the selection of an upper and a lower bank of coils; 4) the relative position of the individual coils in their banks; and 5) the orientation of the coils—are matters of convenience made to demonstrate the functionality of the apparatus. Like the size and type of material selected for the tubing or pipe and the couplers and/or valves, some of these values or parameters are relevant to accurately predicting unit performance.

It is further contemplated that banks of coils may be embedded inside other banks of coils and/or interleaved in order to achieve even greater flow control density providing undamaged polymer by ensuring smooth transitions between the arrangement comprised of multiple banks of coils.

Prior to the precise design and method of manufacturing the apparatus, the determination of unit performance was largely empirical based on rudimentary estimates of a range of expected performance, assembly, bench and field testing, preparation of operational guidelines, and in-service adjustments by a skilled & experienced operator. Advantageously, the apparatus described herein may permit a less skilled and/or experienced operator to implement flow control in a more nearly optimal manner over the life-cycle of the injection field producing better results, in a shorter time, with less expensive resources.

According to a plurality of alternate embodiments, rather than round tubular coils being applied as the conduit through which the stream of polymer fluid flows, it is to be understood that conduit may be of any cross-section, for instance square or rectangular cross-sections. Notably, the shape and internal diameter or cross-sectional area of the conduit are among the variables that the fabricator takes into account. While the mathematical determination of flow rate reduction induced by the resulting product is perhaps easier to carry out with the more familiar round tubular flow characteristics, there is no barrier in nature to the apparatus fabricator applying the present principle of combining frictional drag induction with the decelerative forces of motion through tightly looped conduit so as to enhance the non-turbulent extraction of energy from a polymer stream flowing through a conduit and also providing a variable length flow path within a compact space.

Referring to FIG. 2 there is illustrated an embodiment of an apparatus according to which any suitable heater 250 is mounted in proximity to the banks of coils 110, 120, 130, and 140 (as seen in FIG. 1) so as to prevent aqueous polymer fluid from freezing during cold weather application. Similarly, a housing 260 comprising any insulated structure to protect apparatus 100 from the elements is provided to retain heat and prevent freeze-up. A person of skill in the art would understand that the power output of heater 250 and the R-value of the insulation in the housing 260 may be coordinated with the typical climate at the location where the particular apparatus will be installed. In warmer climates no heater may be required if the thermal insulation provided by the housing is sufficient to protect the coil banks from the convective effects of wind. Similarly, in colder climates a higher power heater may be required with heavier insulation. In the North Western United States, a heater of 1500 watts has been found to operate satisfactorily when combined with a sheet-aluminum housing having R-15 value of insulation.

It is to be understood that an alternate embodiment of the apparatus may be constructed to include a plurality of banks of vertically oriented, elongate elliptical loops of pipe, comprising the conduit element that provides a variable length flow path, and having threaded rather than welded connections. A person of skill in the art would understand that the drag induction calculations must account for the different spatial orientation of the conduit as applied to this embodiment, but the principle remains.

These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not to be construed as being limited by the disclosure. 

1.-15. (canceled)
 16. A flow control apparatus to selectively control a flow of a stream of a polymer fluid during injection at an injection point to enhance recovery of oil from a production well, comprising: an inlet fluidly coupled to a source of the polymer fluid under pressure to receive the polymer fluid; an outlet fluidly coupleable to the injection point; and at least one conduit that provides a selectively variable length flow path fluidly coupled between the inlet and the outlet, the at least one conduit having an associated internal friction that creates a drag on the stream of polymer fluid that passes therethrough wherein the selectively variable length flow path of the at least one conduit controllably decelerates a rate of flow of the stream of polymer fluid through at least a portion of the at least one conduit, the at least one conduit including at least one valve fluidly coupled between the inlet and the outlet, the at least one valve operable to selectively control the length of the flow path through which the stream of polymer fluid pass between the inlet and the outlet, a first tube fluidly coupled between the inlet and the at least one valve; and a second tube fluidly coupleable between the first tube and the outlet by the at least one valve, wherein the at least one valve is operable to selectively fluidly couple the second tube into and out of the flow path between the inlet and the outlet to control the length of the flow path through which the stream of polymer fluid passes between the inlet and the outlet, wherein the improvement comprises the first tube and the second tube each comprises a respective helical coil.
 17. The apparatus of claim 16 wherein the first tube and the second tube are each sections of round tubing.
 18. The apparatus of claim 16 wherein the first and the second tubes are concentrically arranged with respect to one another.
 19. The apparatus of claim 16 wherein the first and the second tubes each include a respective a number of joint-less welded tubes.
 20. A method of operating a flow control apparatus to selectively control a flow of a stream of a polymer fluid during injection at an injection point to enhance recovery of oil from a production well, comprising: providing a source of the polymer fluid under pressure at an inlet fluidly coupled to receive the polymer fluid; and selectively varying a length of a flow path provided by at least one conduit fluidly coupled between the inlet and an outlet, the at least one conduit having an associated internal friction that creates a drag on the stream of polymer fluid that passes therethrough wherein the selectively variable length flow path of the conduit controllably decelerates a rate of flow of the stream of polymer fluid through at least a portion of the conduit, wherein the improvement comprises operating a valve to selectively fluidly couple a second helical coil tube into and out of the flow path with a concentrically arranged first helical coil tube between the inlet and the outlet to control the length of the flow path through which the stream of polymer fluid passes between the inlet and the outlet.
 21. A flow control apparatus to selectively control a flow of a stream of a polymer fluid during injection at an injection point to enhance recovery of oil from a production well, the flow control apparatus comprising: an inlet fluidly coupled to a source of the polymer fluid under pressure to receive the polymer fluid; an outlet fluidly coupleable to the injection point; at least one valve or diverter selectively operable to vary a length of a flow path between the inlet and the outlet, wherein the improvement comprises at least one conduit including a first helical section and a second helical section that provides the selectively variable length flow path fluidly coupled between the inlet and the outlet.
 22. The flow control apparatus of claim 21 wherein the at least one valve or diverter is selectively operable to couple the second helical section into and out of the flow path with the first helical section to vary the length of the flow path between the inlet and the outlet. 